This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for Resin Molding Method For A Coil Used In A Transformer Of A Microwave Oven earlier filed in the Korean Industrial Property Office on Jul. 26, 1999 and there duly assigned Serial No. 30304/1999 and was laid open on Feb. 15, 2001.
The present invention relates to a transformer, and more particularly to a method for forming a resin molding on a coil of a transformer.
Generally, since a high voltage is applied to the coil, a coil used in the transformer of a microwave oven is insulated electrically by an insulating paper or a resin molding. FIG. 1 is an analyzed perspective view for illustrating a method for forming a resin molding for a coil for electrically insulating the coil used in the transformer of the microwave oven in the related art. FIG. 2 is a perspective view for showing the coil covered with a resin molding formed by using the method of FIG. 1.
Referring to the resin molding method for the coil used in the transformer, as shown in FIG. 1, the coil 11 is inserted into a cavity 16 of a metal mold, and then a resin is injected to the coil 11 to form a resin molding 21 on the coil 11 as shown in FIG. 2. In FIG. 1, a reference numeral 12 denotes a connector for drawing out terminal ends from the coil 11. The connector 12 may be connected to the coil 11 for drawing out terminal ends from the coil 11 as shown in FIG. 1, or only two pieces of lines may be drawn out from the coil 11, although such is not shown in the drawings.
The resin molding 21 formed on the coil 11 is required to have a uniform thickness for a good insulation. When the thickness of the resin molding 21 is not uniform, the device can be damaged due to an insulation breaking. Therefore, a plurality of spacing projections 17 are formed on the internal walls of the cavity 16 of the metal mold 15 to keep a uniform interval between the coil 11 and the internal wall. The interval between the coil 11 and the internal wall of the cavity 16 of the metal mold 15 is kept uniform due to the spacing projections 17. Therefore, the resin molding 21 can be formed with a uniform thickness on the coil 11.
However, according to the conventional resin molding method for a coil of a transformer in the microwave oven, when the coil is inserted into the cavity 16 of the metal mold 15, the coil 11 can be damaged due to the spacing projections 17 which are projected from the internal wall of the cavity 16. When a transformer with the scraped coil is used for a long time, the damaged part of the coil 11 breaks easily, and accordingly, the transformer goes out of order. Moreover, the resin molding 21 has recesses 22 formed due to the presence of the spacing projections 17. The resin molding 21 at the recesses 22 may be formed with a thin thickness, or may not be formed at all. In the above cases, the coil 11 is easily damaged. When the coil 11 is damaged and exposed, the insulating status of the coil 11 of the transformer is deteriorated, and accordingly, sparks are generated while the transformer is operated. What is needed is a two step molding process where either an auxiliary spacing apparatus made of resin is first formed around the coil before molding or the coil is twice molded, the first time the molded coil has projections and after the second resin molding, the projections of the first molding process are covered up.
The present invention has been developed to overcome the above problems of the related art, and accordingly it is an object of the present invention to provide a method for forming a resin molding for a coil of a transformer by which the coil is not damaged and the resin molding is formed with an uniform thickness.
The above object is accomplished by a method for forming a resin molding for a coil of a transformer according to the present invention, by inserting a coil into an auxiliary apparatus for spacing; inserting the auxiliary spacing apparatus into a mold; and forming a resin molding for the auxiliary spacing apparatus with the coil by putting a resin into the mold.
The auxiliary spacing apparatus may be formed of the same resin used in the resin molding, or may be a different resin. The auxiliary spacing apparatus has a mesh shape so that the resin used in the resin molding makes enough contact with the coil.
The auxiliary spacing apparatus has preferably a plurality of projections formed on an external surface thereof for ensuring a thickness sufficient to electrically insulate the coil and emit the heat of the coil. Meanwhile, the coil can be directly wounded around the auxiliary spacing apparatus.
The above object is also accomplished by another method for forming a resin molding for a coil of the transformer according to the present invention, by inserting a coil into a primary mold to form a spacing part on the coil; inserting the coil with the spacing part into a secondary mold; and forming a resin molding for the coil with the spacing part by putting a resin into the secondary mold.
The spacing part may be formed of the same resin used in the resin molding or may be different resin. The spacing part has projections with multiple stairs formed on the external surface thereof for preventing from being detached from the resin molding by the secondary mold.